Analytical Sciences

Abstract − Analytical Sciences, 31(1), 7 (2015).

Electrospray Ionization Mass Spectrometry for the Quantification of Inorganic Cations and Anions
Hiroki HOTTA* and Kin-ichi TSUNODA**
*Department of Chemistry, Nara University of Education, Takabatake, Nara 630-8528, Japan
**Department of Chemistry and Chemical Biology, Gunma University, Kiryu 376-8515, Japan
Recent studies from our laboratory on electrospray ionization mass spectrometry (ESI-MS) for the quantification of inorganic cations and anions are reviewed. Metal ions were determined by ESI-MS in negative-ion mode as monovalent negative ions of their aminopolycarboxylate (APC) complexes, where excess amounts of the APC agents were added to sample solutions. Among the APCs studied, we found trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CyDTA, the chemical forms in a complex were expressed as Hncydtan−4) as the best chelating agent. A size exclusion column was used for on-line separation of the metal–APC complexes from matrix salts in samples. Total amounts of Al, Ni, Cu, Zn, and Pb in the biological certified reference materials (CRM), Olive Leaves (BCR-062) and Plankton (BCR-414), and in a soil CRM (JSAC-0401) were successfully determined by the proposed method. Halide ions (X = F, Cl, Br and I) and cyanide (CN) were determined by ESI-MS based on the formation of ternary complexes of metals, chelating agents and the analyte anions. Negative ions of the ternary complexes of group 13 elements, nitrilotriacetic acid (NTA, Hnntan−3), and halides, i.e., [AlF(nta)] for F, and [InX(nta)] for other halides, were measured; the limits of detection (LODs) were 10 nmol dm−3 for F, 0.31 μmol dm−3 for Cl, 3.8 nmol dm−3 for Br, and 1.6 nmol dm−3 for I, respectively. In the case of CN, an LOD of 20 nmol dm−3 was obtained based on measurements of the ternary complex of CuII, CN and 4-(2-pyridylazo)resorcinol (PAR, Hnparn−2), i.e., [63CuII(CN)(par)] (m/z 302). Moreover, quantitative methods for CrVI and CrIII by ESI-MS were developed, where HCrO4 (m/z 117) for CrVI and [CrIII(cydta)] for CrIII were used for measurements.